The invention relates to a process for producing a multilayer body having at least one partially shaped layer made of a material having a high refractive index, and to a multilayer body that is obtainable according to the process. The invention additionally relates, in particular, to a security element for security documents and value documents having such a multilayer body.
Optical security elements are frequently used to render more difficult and, insofar as possible, to prevent, the copying and misuse of documents or products. Thus, optical security elements are frequently used to secure documents, banknotes, credit cards, money cards, identity cards, packagings and the like. It is known here to use optically variable elements which cannot be copied using conventional copying methods. It is also known to equip security elements with layers made of materials having a high refractive index (HRI=High Refractive Index) such as, for example, ZnS, in order to create special optical structures. Whereas full surface-area reflection layers made from HRI materials can be produced relatively easily by common application methods such as, for example, sputtering, vapor deposition or the like, the production of structured, partial HRI layers is significantly more complex.
HRI layers can serve as reflection layers because, together with adjacent varnish layers, which usually have refractive indices of medium magnitude, e.g. 1.5, they form an optical boundary layer. This optical boundary layer renders structures at this boundary layer visible, although the structures are embedded between the two layers.
The more production steps that are provided for the production of the security element, the greater the importance that attaches to the register accuracy of the individual process steps, or to the accuracy of positioning of the individual tools, in the formation of the security element, in respect of features or structures already present on the security element.
The term “register accuracy” originates from printing technology. Register marks on are used there, which are applied to various layers or plies. These register marks make it very easy to set the exact relative ply accuracy of the plies or layers in relation to each other, and thereby to achieve a so-called register accuracy. “In register” thus means that the respective plies or layers are aligned with sufficient ply accuracy in relation to each other by means of the register marks. These terms are used in this sense in the following; i.e. it is a matter of aligning layers lying one on top of the other as accurately as possible relative to each other and arranging them “in register”.